Unimog Club UK

Little wire would be from the sender unit I would think. Crimp a new terminal to it and see if it works when it's connected?

As for the air. Mine runs slightly over pressure but only by about 1/2 bar. The regulator on my 406 is on the passenger side behind the alcohol anti freeze unit. There's a small screw in the top of it that adjusts the blow off pressure, although I would think something is stuck for it to climb that high. I haven't taken mine apart to know how it works but it sounds like you need to!